When you're so fucked up that time itself has no meaning at all. Looking for the right candybar at Walgreens can take hours when you're geeking. You can spend a day trying to fold some origami model, or solve a math problem, or read a single paragraph.
Also related to tweaking.
When tweaking AND geeking, this time contraction is combined with a feverish hurry and awareness of your own "meth stench," not to mention a belief that what you are doing is of the utmost importance, and is not to be disturbed by anyone.

I was geeking last night - I must have de-childproofed about 20 lighters!

Taking a dose of prescription ADD medication (adderall, vyvanse, ritalin, dex) when one is not prescribed as such, and proceeding to do procrastinated schoolwork much more efficiently than if one hadn't taken the medication. Sometimes you can use it to stay up all night typing furiously or studying for exams. Geeking is the academic cousin of Tweaking.

I have a term paper due tomorrow that I haven't even started, I'm gonna be geeking all night.